A New Method of Calculating Electrical Conductivity With Applications to Natural Waters
Publication year: 2011
Source: Geochimica et Cosmochimica Acta, Available online 21 October 2011
R. Blaine McCleskey, D. Kirk Nordstrom, Joseph N. Ryan, James W. Ball
A new method is presented for calculating the electrical conductivity of natural waters that is accurate over a large range of effective ionic strength (0.0004 mol kg– 0.7 mol kg), temperature (0 °C – 95 °C), pH (1 – 10), and conductivity (30 μS cm– 70,000 μS cm). The method incorporates a reliable set of equations to calculate the ionic molal conductivities of cations and anions (H, Li, Na, K, Cs,, Mg, Ca, Sr, Ba, F, Cl, Br,,, and OH), environmentally important trace metals (Al, Cu, Fe, Fe, Mn, and Zn), and ion pairs, and. These equations are based on new electrical conductivity measurements for electrolytes found in a wide range of natural waters. In addition, the method is coupled to a geochemical speciation model that is used to calculate the speciated concentrations required for accurate conductivity calculations. The method was thoroughly tested by calculating the conductivities of 1,593 natural water samples and the mean difference between the calculated and measured conductivities was -0.7% ± 5%. Many of the samples tested were selected to determine the limits of the method and include acid mine waters, geothermal waters, seawater, dilute mountain waters, and river water impacted by municipal waste water. Transport numbers were calculated and H, Na, Ca, Mg,, K, Cl,, F, Al, Fe,, andsubstantially contributed (>10%) to the conductivity of at least one of the samples. Conductivity imbalance in conjunction with charge imbalance can be used to identify whether a cation or an anion measurement is likely in error, thereby providing an additional quality assurance/quality control constraint on water analyses.
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